Red-emitting phosphors based on complex fluoride materials activated by Mn4+, such as those described in U.S. Pat. Nos. 7,358,542, 7,497,973, and 7,648,649, can be utilized in combination with yellow/green emitting phosphors such as YAG:Ce or other garnet compositions to achieve warm white light (CCTs<5000 K on the blackbody locus, color rendering index (CRI>80) from a blue LED, equivalent to that produced by current fluorescent, incandescent and halogen lamps. These materials absorb blue light strongly and efficiently emit between about 610-635 nanometers (nm) with little deep red/NIR emission. Therefore, luminous efficacy is maximized compared to red phosphors that have significant emission in the deeper red where eye sensitivity is poor. Quantum efficiency can exceed to 85% under blue (440-460 nm) excitation.
While the efficacy and CRI of lighting systems using Mn4+ activated (or doped) fluoride hosts can be quite high, one potential limitation is their susceptibility to degradation under fabrication and use conditions, for example under high temperature and humidity. It is possible to reduce this degradation using post-synthesis processing steps, as described in U.S. Pat. No. 8,252,613. However, development of other methods for improving stability of the materials is desirable.